1080. Mechanism of the conversion of α-thujadicarboxylic ester into tanacetophorone

Crombie, L.; Mitchard, D. A.

doi:10.1039/jr9640005640

Cited by 5 publications

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“…with the sample described above, 170 "C (total yield from the cyclohexenone, 90%). (23).-A sol ution of chromic acid, prepared by dissolving chromium trioxide (25 g) in 2~-sulphuric acid (70 ml) was added slowly to one of the preceding hydroxycyclohexanone (12.0 g) in acetone (150 ml). The mixture was stirred at 20 "C for 2 h, and then poured into water.…”

Section: -Hy~roxynieth~~l-455-trirr1etli~~lcyclolrc~x-2-en-i-one (20)-mentioning

confidence: 99%

“…Autoxidation of the keto-acid (23) in the presence of potassium t-butoxide gave the diosphenol (24). This on treatment with dilute alkali, underwent the expected benzylic acid type of rearrangement with ring contraction.…”

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confidence: 99%

“…Treatment of the product with acid yielded the crystalline cyclohexenone (20) which was hydrogenated catalytically to give a mixture of the required cyclohexanone (22) and the cyclic ether (21). The latter on treatment with dilute acid was converted almost quantitatively into the cyclohexanone (22), which was oxidised with chromic acid to give the keto-acid (23). This was stable to heat, thus excluding the P-keto-acid structure that would have been obtained had the initial reaction with the P-diketone (18) given the isomeric enol ether (29).…”

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confidence: 99%

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Carotenoids and related compounds. Part 37. Stereochemistry and synthesis of capsorubin

Bowden¹,

Cooper²,

Harris³

et al. 1983

J. Chem. Soc., Perkin Trans. 1

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The two oxygen substituents in the end groups of capsorubin were shown to be trans to one another by synthesis of optically inactive forms of the carotenoid, and of the isomers which have the corresponding cis-structure. The 3S,5R,3'S,5'R configuration thus established for the natural carotenoid was confirmed by synthesis of this stereoisomer from (+)-camphor.Cryptocapsin has the 3'S,5'R configuration, and the racemic form has been synthesised. Capsanthin has the 3R,3'S,5'R configuration.

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Section: -Hy~roxynieth~~l-455-trirr1etli~~lcyclolrc~x-2-en-i-one (20)-mentioning

confidence: 99%

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Carotenoids and related compounds. Part 37. Stereochemistry and synthesis of capsorubin

Bowden¹,

Cooper²,

Harris³

et al. 1983

J. Chem. Soc., Perkin Trans. 1

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TheDieckmann Condensation (Including theThorpe‐Ziegler Condensation)

Schaefer

Bloomfield

2011

Organic Reactions

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The Dieckman condensation is an acetoacetic ester condensation in which a dicarboxylic ester is cyclized to a beta‐ketonic ester through the action of a base. The dicarboxylic ester must have at least one alpha‐hydrogen atom and the carbalkoxy groups must be situated that cyclization will result in a 4‐membered ring or larger ring. Discovery and development of the reaction are generally credited to Dieckmann, who found that heating an adipic or a pimelic ester with sodium and a trace alcohol led to cyclization with formation of a cyclopentanone or a cyclohexanone. The Dieckmann condensation has proved useful for the preparation of a variety of carbocyclic and heterocyclic ketones and has been extended to the synthesis of 7 and 8‐membered rings.

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Evaluation of Strain Effects on the Reactivity of Small Rings

Stirling

1981

Israel Journal of Chemistry

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Abstract. The qualitative effect of ring strain on the reactivity of small ring systems is briefly reviewed. It is pointed out that nucleofugalities of groups cannot be measured for nucleophilic substitution but that such measurements are possible for activated eliminations. Application of the techniques for determination of nucleofugality to eliminative fission of small strained rings shows that nucleofugality is very greatly enhanced. The extent of enhancement cannot be determined for epoxides, but has been determined for cyclopropanes, the results showing that about 60% of the ring strain energy is released in the transition state of ring fission. Catalysis of ring fission requires very specific placement of proton donor groups; gem-dimethyl substitution raises the enthalpy of the transition state for eliminative fission of cyclopropanes.This account considers the question: How much does ring strain energy contribute to reactivity in heterolytic ring cleavage? A striking feature of small ring chemistry is that in spite of the fact that ring strain is a major factor in controlling the reactivity of small rings, almost no quantitative data relating to this question is available. This account describes quantitative answers to this question for the first time and, within the compass of the account, the results have a bias towards recent work in these laboratories.strain energy that appears in reducing the energy of activation of the ring c1earage reaction?There are two serious difficulties in answering such a question. First, unstrained acyclic analogues, with which to compare the reactivity of strained cyclic systems, are not readily available particularly as the leaving groups must be at least two-coordinate. Second, the relationship between reactivity in nucleophilic substitution and 'leaving group ability' in a quantitative sense is unexplored. RING STRAIN AND SUBSTITUfIVE CLEAVAGE OF SMALL RINGSRing strain energies are summarised in Table 1. The very large strain energies of three-and four-membered rings are interpretable as arising from inefficient bonding by overlap of orbitals of high p-character.' These large strain energies are clearly responsible for reactions shown particularly by three-and four-membered ring systems, but not by their acyclic (unstrained) analogues or by larger ring systems of lesser strain. Typical of such reactions are nucleophilic substitutions on cyclopropanes and epoxides, Eq. (I), (Fig. 1). Such reactions, involving SN2 displacements of uncharged oxygen and carbon leaving groups, do not have analogues in acyclic or larger ring systems (Eq. (2». Dimethyl ether, for example, is not susceptible to nucleophilic substitution with displacement of methoxide ion. In alkaline hydrolysis of an epoxide, the strain of the ring reduces the energy of activation for the reaction by transforming the 'poor' alkoxide leaving group into a 'good' leaving group. The intriguing question is, therefore, how much does the (known) strain of the oxiran ring promote displacement of an alkoxide leaving group...

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1080. Mechanism of the conversion of α-thujadicarboxylic ester into tanacetophorone

Cited by 5 publications

References 0 publications

Carotenoids and related compounds. Part 37. Stereochemistry and synthesis of capsorubin

Carotenoids and related compounds. Part 37. Stereochemistry and synthesis of capsorubin

TheDieckmann Condensation (Including theThorpe‐Ziegler Condensation)

Evaluation of Strain Effects on the Reactivity of Small Rings

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